Stable oxygen isotope (S18O) analysis of archaeological shellfish remains combined with sclerochronology can be used to precisely reconstruct past sea surface temperature (pSST), season(s) of shellfish collection, and thus the season(s) of archaeological site occupation. Our study tests if S18Oshell and sclerochronological analyses of marine bivalve species Leukoma staminea - with previously unassessed seasonality and pSST potential - can provide additional insights not captured by the better studied species, Saxidmous gigantea in British Columbia (BC, Canada). We analyzed live-collected L. staminea and S. gigantea shells from Sechelt, BC, and compared results to archaeological shell data from Powell River, BC, in the territory of the Tla'amin First Nation (1065 to 797 cal. B. P.). The seasonality of shellfish harvest differed between species, with S. gigantea preferentially collected in the spring, whereas L. staminea collected year-round. This highlights that sole-species seasonality studies may miss important variability in harvesting strategies. Additionally, comparisons between instrumental (5.7 to 20.4 degrees C) and reconstructed SST from modern L. staminea S18Oshell (5.6 to 18.4 degrees C) showed good agreement in annual range. Our results indicate that archaeological S. gigantea record a wider range of pSST (-1.6 to 22.9 degrees C) than archaeological L. staminea (5.8 to 25.9 degrees C), suggesting that S. gigantea may be a more sensitive palaeotemperature recorder. Further, we found that using the same reconstructed S18Owater value for both species in pSST reconstruction caused an overestimation of temperature. Accordingly, we argue that it is critical to calibrate the equation with corresponding species-specific S18Oshell values, regardless of both having aragonite mineral structures. Our study highlights the potential of L. staminea to broaden seasonality interpretations while clarifying that its use for pSST reconstruction may not capture the lower range of temperature.

Sea-ice loss and increasing unpredictability have disturbed and harmed Arctic peoples and ecosystems. In addition, studies demonstrate that sea ice plays a key role in climate variability and air–sea CO2 exchanges. Sea-ice data sets provide environmental baselines, validate proxies and models, and serve in regional and temporal comparisons. Accordingly, sea-ice and sea-ice–related variables are particularly valuable in climate modeling, paleoclimatology, and ecology to document past and present environmental changes and predict future outcomes. This article provides an overview of modern, historical, and long-term proxy sea-ice data sets that cover the last millennium. We describe available Arctic sea-ice data sources, discuss each data set’s strengths and limitations, and compare multisourced Arctic sea-ice histories in different regions. We conclude with remarks on the impacts of internal forcing from natural feedbacks and oscillations versus anthropogenic impacts on sea-ice variability. We draw upon remaining uncertainties regarding causes of past sea-ice variability and advocate for continued use of multiple data sources in sea-ice reconstruction–related studies and further development of a multisourced past sea-ice data network.

Abstract Given sea ice's importance in global climate regulation, fully understanding the role of natural temperature and atmospheric patterns like the Arctic Oscillation (AO), North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO) in its variability is critical. While instrumental AMO and reliable AO records are available since the mid‐1800s and 1958, respectively, satellite sea‐ice concentration data sets start only in 1979, limiting the shared timespan to study their interplay. Growth increments of the coralline algae, Clathromorphum compactum, can provide sea‐ice proxy information for years prior to 1979. We present a seasonal 210‐year algal record from Lancaster Sound in the Canadian Arctic Archipelago capturing low frequency AMO/NAO variability and high frequency interannual AO/NAO prior to 2000. We suggest that sea‐ice variability here is strongly coupled to these large‐scale climate processes, and that sea‐ice cover was greater and the AO more negative in the early and late 19th century compared to the 20th.

The Sechelt inlet system (SIS), situated on the inner Sunshine Coast of British Columbia, lies within the territory of the shishalh Nation. This study focuses on similar to 1000 years of shishalh shellfish harvesting from 930-0 cal. BP. Specifically, we investigated the seasonal timing of shellfish collection, relative shellfish harvesting pressure and paleo-temperature reconstruction at four archaeological sites. Thirty archaeological butter clam shells (Saxidomus gigantea) from the SIS underwent high-resolution shell oxygen isotope (delta O-18) analysis and 662 individual archaeological shell fragments were analysed for growth stage determination. The delta O-18 results showed a pattern of year-round collection with an emphasis on spring collection at village sites. Results from shell growth stage analysis suggest an intensive pattern of shellfish harvesting in the region, regardless of the site type. Archaeological shells show a larger delta O-18(shell) range, possibly reflecting a greater sea surface temperature amplitude than modern shells (i.e. a difference of similar to 6.5 degrees C; modern range: similar to 3.7-20.4 degrees C; archaeological range: similar to -0.8-22.4 degrees C). We contextualise our results with previous studies of seasonal timing and intensity of shellfish harvesting from the Pacific Northwest Coast, while interpreting these new data in the context of shishalh occupation and landscape use.

The Atlantic Multidecadal Oscillation (AMO), Arctic Oscillation (AO), and related North Atlantic Oscillation (NAO) have been linked to multidecadal, decadal, and/or interannual sea-ice variability in the arctic, but their relative influences are still under evaluation. While instrumental AMO and reliable AO records are available since the mid-1800s and 1958, respectively, satellite sea-ice concentration datasets start only in 1979, limiting the shared timespan to study their interplay. Growth increments of the coralline algae, Clathromorphum compactum, can provide sea-ice proxy information for years prior to 1979. We present a seasonal 210-year algal record from Lancaster Sound in the Canadian Arctic Archipelago capturing low frequency AMO variability and high frequency interannual AO/NAO prior to 2000. We suggest that sea-ice variability here is strongly coupled to these large-scale climate processes, and that sea-ice cover was greater and the AO more negative in the early and late 19th century compared to the 20th.

Paleoclimate and paleoenvironmental reconstructions from increment-yielding archives strongly depend on precise age models. Like bivalves, corals, trees, and speleothems, the coralline alga Clathromorphum compactum produces annual growth increments and shows considerable promise as an environmental archive for arctic and subarctic regions. Though their growth increment widths correlate with temperature and sea ice cover in high Arctic regions, existing timeseries have not been crossdated. In fact, previous studies have shown a lack of inter-sample correlation in non-crossdated timeseries suggesting possible age model dating errors. Here, we use dendrochronology crossdating techniques and COFECHA software to ensure and validate synchrony between C. compactum timeseries (<141 years) from three specimens collected near Beechey Island, Nunavut, Canada. Results showed that non-crossdated timeseries constructed by four coralline red algae researchers using annual increments of the same C. compactum samples were highly variable and showcase the likelihood of dating errors in non-crossdated timeseries. Crossdating improved inter-series correlations, and correlations to sea ice-related records, suggesting that at least three crossdated timeseries are required to isolate paleoclimate signals. Our findings suggest that future reconstructions with C. compactum should employ crossdating techniques to reduce dating errors and allow for more precise climate reconstructions. Lay Abstract Long-term environmental records provide a critical baseline to examine how humans have impacted Earth’s natural climate. An important piece to consider is sea ice’s role in natural climate variability because its brightness limits warming by reflecting solar irradiation back to space. However, instrumental records of sea ice rarely extend beyond the early satellite era (late 1970s), limiting our understanding of how sea ice affects natural climate variability in the preindustrial era. A lack of historical baseline prompted the development of sea ice proxies, including the long-lived marine alga, Clathromorphum compactum. Similar to tree-rings, C. compactum produces a new mineralized layer each year, and layer thicknesses have been shown to respond to sea ice cover, making them useful to record long-term sea ice variability. However, a recent study showed that records had replicability problems, maybe due to dating mistakes. Our study applies tree-ring dating methods (dendrochronology) to match annual algal growth layers across algal specimens. Results showed that these new methods reduced dating errors, allowing for more precise past sea ice cover reconstructions.

Arctic sea ice cover has been steeply declining since the onset of satellite observations in the late 1970s. However, the available annually resolved sea ice data before this time are limited. Here, we evaluated the suitability of annual trace element (Mg/Ca) ratios and growth increments from the long‐lived annual increment‐forming benthic coralline red alga, Clathromorphum compactum, as high‐resolution sea ice cover archive. It has previously been shown that the growth of C. compactum is strongly light controlled and therefore greatly limited during the polar night and underneath sea ice cover. We compare algal data from 11 sites collected throughout the Canadian Arctic, Greenland, and Svalbard, with satellite sea ice data. Our results suggested that algal growth anomalies most often produced better correlations to sea ice concentration than Mg/Ca ratios or when averaging growth and Mg/Ca anomalies. High Arctic regions with persistently higher sea ice concentrations and shorter ice‐free seasons showed the strongest correlations between algal growth anomalies and satellite sea ice concentration over the study period (1979–2015). At sites where ice breakup took place before the return of sufficient solar irradiance, algal growth was most strongly tied to a combination of solar irradiance and other factors such as temperature, suspended sediments, phytoplankton blooms, and cloud cover. These data are the only annually resolved in situ marine proxy data known to date and are of utmost importance to gain a better understanding of the sea ice system and to project future sea ice conditions.

Earth and Space Science Open Archive This work has been accepted for publication in Paleoceanography and Paleoclimatology. Version of RecordESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary. Learn more about preprints. preprintOpen AccessYou are viewing the latest version by default [v1]Suitability of the Coralline Alga Clathromorphum compactum as an Arctic Archive for Past Sea ice CoverAuthorsNatashaLeclerciDJochenHalfarSteffenHetzingerPhoebeChanWalterAdeyAlexandraTsayEricBrossierAndreasKronziDSee all authors Natasha LeclerciDCorresponding Author• Submitting AuthorUniversity of TorontoiDhttps://orcid.org/0000-0002-0570-4790view email addressThe email was not providedcopy email addressJochen HalfarUniversity of Toronto at Mississaugaview email addressThe email was not providedcopy email addressSteffen HetzingerUniversität Hamburgview email addressThe email was not providedcopy email addressPhoebe ChanUniversity of Bergen and Bjerknes Centre for Climate Researchview email addressThe email was not providedcopy email addressWalter AdeyDepartment of Botany, Smithsonian Institutionview email addressThe email was not providedcopy email addressAlexandra TsayUniversity of Genevaview email addressThe email was not providedcopy email addressEric BrossierAssociation Nord-Estview email addressThe email was not providedcopy email addressAndreas KronziDUniversitaet GoettingeniDhttps://orcid.org/0000-0001-5655-4633view email addressThe email was not providedcopy email address